The present invention relates to a method of lining a steel-making furnace, with special emphasis on those areas of the furnace which are subjected to heavy wear during operation of the furnace. The invention also relates to a furnace lined by this method.
Up to now, the wall area of electric steel-making furnaces was lined with a layer of regular bricks, for example, magnesium oxide bricks, and then an overlayer of carbon-containing bricks, particularly, tar-containing magnesium oxide and/or dolomite bricks. The bottom area of the electric furnace was lined with a safety layer of magnesium oxide bricks, and a refractory material was placed over this safety layer and also the carbon-containing bricks in the lower portion of the wall area. FIG. 4 of the drawings shows this construction of a conventional lining for an electric steel-making furnace. It also shows the steel bath level and the area of the wall which is subjected to particularly heavy wear, as will be discussed in more detail later on. In the case of such conventional electric steel-making furnace linings, it has been necessary to frequently repair those areas of the wall which are subjected to heavy wear, sometimes after each melting process.
In such a melting process, in an electric furnace of medium capacity, at the beginning of the melting process scrap iron is placed in the furnace with a scrap-iron basket, the electrodes are lowered onto the scrap iron, and the scrap iron is melted. The melting time is on the order of 30 minutes. Then, a second batch of scrap iron is placed in the furnace, and melted in about 30 minutes. Finally, a third batch of scrap iron is placed in the furnace, and melted in 30 minutes, giving a total melting time for all three batches of about 90 minutes. When the capacity of the furnace has been reached, in this case after melting three batches of scrap iron, the metallurgical work is finished, leaving only the required analyses. After the analyses have been completed, tapping takes place.
U.S. Pat. No. 3,832,478 discloses a method of avoiding premature wear of the critical areas of steel-making furnaces, particularly electric furnaces, by spraying a composition onto the hot faces of the bricks lining the furnace before operating the furnace. The patent indicates that a mixture of magnesia and dolomite may be sprayed over the critical wear areas. However, it is first necessary to heat up the critical wall areas. Furthermore, it is necessary to encase each of the bricks in the critical areas in a steel sheet projecting outward from the hot faces of the bricks, to serve as receptacles and anchors to retain the spraying composition.
U.S. Pat. No. 3,994,676 discloses a method of protecting critical wear areas in the lining of a basic oxygen furnace. In this method, tie rods are mounted on the bricks, to hold a grid, onto which a composition is sprayed. The patent indicates that pulverulent magnesia, magnesite or dolomite, in the form of a sprayable slurry may be used in protecting the critical wear areas.
Industrial Heating, Vol. 30, 1963, pages 1120-1126 discloses spraying compositions which are based on periclase and bonded with sodium phosphates. If necessary, the composition may also contain clay, for example, bentonite, as a plastifying agent. This publication indicates that the compositions can be sprayed onto either hot or cold surfaces, but does not provide any information concerning its use with electric furnaces, or any information concerning special conditions which must be observed.
German patent publication 1,571,608 discloses compositions containing sodium phosphate as bonding agent, for spraying onto areas of heavy use. The components of the composition must have a very specific grain size. Bentonite, in an amount of up to 2%, can be used as a plastifying agent. However, after the composition is sprayed onto the cold surfaces, the surfaces must be heated slightly, and slowly.